System, device and method for cutting steel plate

ABSTRACT

A system for cutting steel plate, in particular for cutting the bottom and/or the wall of an oil storage tank, comprising a hydraulic or pneumatic pump and a movable cutting device comprising a hydraulic or pneumatic motor for moving the cutting device, wherein the pump and the motor are hydraulically or pneumatically interconnected by means of hoses.

The invention relates to a system for cutting steel plate, in particularfor cutting the bottom and/or the wall of an oil storage tank. Althoughthe invention will be described in relation to the cutting of steelplate, and in particular to the cutting of the bottom and/or the wall ofan oil storage tank, the invention can also be used for cutting othermaterials.

An oil storage tank as used in the oil-processing industry, for example,is generally built up of a steel, disc-shaped bottom plate, a steel walland the roof, which may or may not be vertically movable. Corrosion andwear make it necessary to replace the plate members in whole or in parton a regular basis. To that end, the plate members in question are cutout and removed, after which new plate members are welded in position inor over the hole. So far, said cutting out has been carried out by meansof cutting torches wielded by skilled workers who enter the storagetank, to which end they first cut a hole in the wall of the (empty)storage tank in many cases.

A major drawback of this method is the fact that the work is tiring forthe workers, but above all this method potentially constitutes asignificant health hazard. Not only may the prolonged inhalation ofresidual oil vapours in the storage tank cause damage to the workers'health, but in addition there is a direct risk of explosion. Frequently,jet flames and explosions occur in the storage tank when this method isused. Consequently, regulations prescribe that the workers carry out thework in sturdy protective clothing.

Consequently, there is a need for a system for cutting steel plate whichis less hazardous to the workers' health, and/or which renders theremoval of steel plate members simpler and/or cheaper.

To that end the system comprises a hydraulic or pneumatic pump and amovable cutting device comprising a hydraulic or pneumatic motor formoving the cutting device, with the pump and the motor beinghydraulically or pneumatically interconnected by means of hoses. Thecutting device can thus move independently through the oil storage tank,possibly guided and operated by an operator, whilst the pump is disposedoutside the tank. Since no sparks or flames are caused by the motorinside the oil tank, the risk of jet flames and explosions occurring isminimised. The device may also be adapted for operation by remotecontrol, or it may carry out the cutting operation entirely inaccordance with a preprogrammed control programme, so that the presenceof an operator in the tank is not required, which further enhances thesafety level.

The cutting device preferably comprises at least one nozzle forsquirting an abrasive liquid under high pressure against and through theplate. This manner of cutting through plate helps to further reduce therisk of explosion.

The nozzle is preferably supported by at least one wheel, which cantravel over the steel plate. It is important that a precisely definedspacing be maintained between the nozzle and the plate in the case ofabrasive cutting. The nozzle is preferably spring-connected to thedriven portion of the cutting device. In this way the wheel is urgedinto contact with the plate under all circumstances, and anyirregularities in the plate, such as weld seams, do not stand in the wayof obtaining a regular cut in the plate.

The cutting device is preferably fitted with two spaced-apart nozzles,in such a manner that the cutting device is capable of cutting a stripfrom the steel plate in one movement. Furthermore preferably, thecutting device comprises a container for an abrasive agent.

A regular and precisely defined velocity of movement is very important,since otherwise the plate might not be fully cut through at some points.To that end the cutting device is fitted with caterpillar tracks formoving the device. Moreover, the transmission ratio between the motorand the wheels is such that the velocity of movement of the device willpreferably be less than 0.5 m/s, more preferably less than 0.1 m/s, evenmore preferably less than 0.06 m/s, with an engine speed of about 3000rpm or a hydraulic output of about 25 l/min.

The invention also relates to a cutting device for cutting steel plate,in particular for cutting the bottom and/or the wall of an oil storagetank, comprising at least one nozzle for squirting an abrasive liquidunder high pressure against and through the plate, and a motor formoving the cutting device. In this simple embodiment of the invention,the motor may be any type of motor, for example an electric motor or acombustion motor. Preferably, however, a hydraulic or pneumatic motor isused for cutting the bottom or the wall of an oil storage tank, whichmotor is hydraulically on pneumatically connected, by means of hoses, toa separate hydraulic or pneumatic pump disposed outside the tank.

The invention furthermore relates to a method for cutting the bottomand/or the wall of a storage tank, wherein a cutting device is movedover the bottom of the storage tank by means of a motor during thecutting operation. Preferably, said cutting is effected by squirting anabrasive liquid under high pressure against and through the bottomand/or the wall. The abrasive liquid preferably contains stand and/orgarnet. Furthermore, the cutting device is preferably hydraulically orpneumatically driven, to which end a hydraulic or pneumatic pump isdisposed outside the storage tank, which pump is connected to the motor.

In a special embodiment of the method according to the invention, thecutting device abuts against the wall of the storage tank while movingthrough the storage tank, with the wall acting as a guide for thecutting device. In this way, the bottom is cut loose from the wall inone operation. In order to enable the removal of the loose bottom fromthe tank, it will be necessary to cut the loose bottom into strips,which strips can subsequently be removed through an opening in the wall.

The invention will now be explained in more detail by means of anembodiment as shown in the Figures, in which:

FIG. 1 is a perspective view of a system for cutting steel plate, whichcomprises a cutting device and a hydraulic pump unit;

FIG. 2 is a perspective view of the cutting device that is shown in FIG.1;

FIG. 3 is a perspective view of a detail of the cutting device that isshown in FIG. 2; and

FIGS. 4 a and 4 b are schematic views of a bottom of an oil storage tankand a cutting device.

According to FIGS. 1 and 2, a system for cutting steel plate comprises acutting device 1 and a hydraulic pump device 2. The hydraulic pumpdevice 2 is provided with caterpillar tracks 3, which make it mobile.The pump device 1 is connected, via hoses, to a hydraulic motor 4 thatfunctions to drive the cutting device 1, which motor 4 is to that endprovided with hydraulic connections 5, 6 (see FIG. 3). The front wheels7 of the cutting device 1 are driven via a transmission, which will bediscussed with reference to FIG. 3. Caterpillar tracks 8 are passed overthe driven wheels 7, which tracks are further tensioned by idle wheels9.

The motor 4, the transmission and the wheels 7, 9 are all mounted on aframe 10.

The frame 10 comprises two beams 11 extending in the direction ofmovement, substantially along the entire length of the cutting device 1,on which beams two laterally extending arms 12 are movably mounted.

Rods 13 extend downwards from said arms 12, to which rods travellinggears 15 are connected by means of telescopic spring mechanisms 14. Thetravelling gears 15 each comprise two wheels 16, between which a nozzle17 is suspended. During operation, the wheels 16 are pushed against thesurface to be cut by the telescopic spring mechanism 14, with apredetermined constant spacing being maintained between the nozzle 17and said surface. Said spacing will generally range from 2 to 10 mm.

The nozzle 17 is connected to a high-pressure water source, for examplea pump device 2, by means of a hose 18, and to the container 20 by meansof a hose 19. In use, the container 20 is filled with an abrasive agent,such as sand or garnet, which is sucked into a mixing chamber 21 of thenozzle 17 as a result of a sub-atmospheric pressure prevailing therein,in which mixing chamber it is mixed with the water. Said mixture is thussquirted against and through the surface to be cut, during whichoperation the cutting device is moved ahead at a constant velocity ofmovement. The water pressure must generally be set at a level of500-4000 bar, depending on the thickness of the material and the type ofmaterial.

According to FIG. 3, the transmission between the hydraulic motor 4 andthe driven wheels 7 comprises a continuously variable transmissionmechanism 22, which is connected to the hydraulic motor 4 by means of adriving belt 25. The transmission mechanism 22 can be controlled bymeans of a control rod 23, by means of which both the velocity ofmovement and the direction of movement of the cutting device 1 can beset.

The driven shafts-24 are connected to the transmission mechanism 22 viaa controlled slip differential 28, which differential can be locked bymeans of a control button 29, so that a straight line of movement of thedevice can be maintained in use. This latter aspect is important inconnection with any irregularities in the surface over which the device1 is being moved. The driven shafts 24 are connected to the drivenwheels 7 by means of two further driving belts 26, 27.

The dimensions of the transmission 2 have been selected such that thevelocity of movement of the cutting device 1 is maximally about 5.5 cm/swith a hydraulic output of the hydraulic motor 4 of 25 l/min at about3000 rpm of said motor. The pressure being delivered by the hydraulicpump device 2 is about 60 bar in that case.

Because the velocity of movement of the cutting device 1 is too low formoving the device quickly between two working places, the device 1 isprovided with three castors 30 that can be moved by means of a crank 31to such an extent that the caterpillar tracks 8 as well as thetravelling units 15 are lifted clear of the surface and the device 1 canbe moved manually. Furthermore, the frame 10 of the device 1 is providedwith horizontally rotating guide wheels 32 in the corner points, whosefunction will be explained with reference to FIG. 4 b.

FIG. 4 a shows in schematic, top plan view the manner in which a bottomplate 33 of an oil storage tank is cut into strips by a cutting device1. The pump device 2 (not shown) is disposed outside the oil storagetank, and it is connected to the cutting device 1 by means of the hoses4, 18. The cutting device 1 is positioned against the wall 34 of thetank with its front or rear side for the purpose of cutting a strip fromthe bottom 2. The two arms 12 are moved over the beams 11 to a positionas close to the wall 3 as possible, after which the pump device 2 is putinto operation, causing the cutting device to move slowly away from thewall 3. At the same time, the high pressure water pump is put intooperation, and a start is made with the cutting of the bottom plate 2along the lines 35, 36. Once the cutting device 1 has moved a sufficientdistance away from the wall 3, it is moved back over a distancecorresponding to the length of the cutting device 1, and the arms 12 aremoved entirely to the front over the beams 11. The device 1 is set goingagain, and the strip is cut out in its entirety in the directionindicated by the arrow 37, until the opposite side is reached.

FIG. 4 b shows how the device 1 can be used for cutting the bottom loosealong a circular line along the wall 34. This may be done after orbefore the cutting of the strips as shown in FIG. 4 a. In order to doso, one of the two arms 12 and the nozzle 17 connected therewith areremoved, and two of the horizontally rotating guide wheels 32 present onone side of the device 1 are placed into abutment with the wall 34. Whenthe cutting device is now set moving in the direction indicated by thearrow 38, and the water containing the abrasive agent is squirtedthrough the remaining nozzle 17, the bottom 33 will be cut through alongthe line 39. It should be considered that FIGS. 4 a and 4 b are notdrawn to scale, and that in practice the dimensions of the cuttingdevice 1 are much smaller when compared to the cross-sectional dimensionof the bottom 33, so that only a relatively narrow strip will remainalong the wall 34.

The device 1 that is shown in the Figures comprises a frame 10 which ismade in one piece. In order to be able to move the device 1 through asmall opening in the oil storage tank, however, it is preferred to use aframe assembled from detachable parts, so that the cutting device 1 canbe inserted into the storage tank in small parts and subsequently beassembled therein.

Although this is not shown in the Figures, the cutting device may alsobe provided with a hydraulic lift, on which a nozzle 17 is mounted. Saidlift can be moved up and down along the wall 34, so that also said wall34 can be cut into pieces.

Although at least one person must be present in the oil storage tank foroperating the device 1 that is shown in this embodiment, the device 1may also be adapted for being operated by remote control, or a controlprogramme may be used, so that the device 1 will automatically followthe correct path for achieving the desired result.

1. A system for cutting steel plate, comprising: at least one of ahydraulic and pneumatic pump; and a cutting device including at leastone of a hydraulic and pneumatic motor for driving the cutting device,wherein the pump and the motor are at least one of hydraulically andpneumatically interconnected via hoses, wherein the cutting device ismovable independently relative to the steel plate by way of said motor.2. A system according to claim 1, wherein the cutting device includes atleast one nozzle for squirting an abrasive liquid under high pressureagainst and through the plate.
 3. A system according to claim 2, whereinthe nozzle is supported by at least one wheel, which can travel over thesteel plate.
 4. A system according to claim 2, wherein the nozzle isspring-connected to the driven portion of the cutting device.
 5. Asystem according to claim 2, wherein the cutting device is fitted withtwo spaced-apart nozzles, in such a manner that the cutting device iscapable of cutting a strip from the steel plate in one movement.
 6. Asystem according to claim 1, wherein the cutting device includes acontainer for an abrasive agent.
 7. A system according to claims 1,wherein the cutting device is fitted with caterpillar tracks for movingthe device.
 8. A system according to claim 1, wherein the transmissionratio is such that the velocity of movement of the device will be lessthan 0.5 m/s, with at least one of an engine speed of about 3000 rpm anda hydraulic output of about 25 l/min.
 9. A cutting device for cuttingsteel plate, comprising: at least one nozzle for squirting an abrasiveliquid under high pressure against and through the plate; and at leastone of a hydraulic and pneumatic motor for driving the cutting device,wherein the cutting device is movable independently relative to thesteel plate by way of said motor.
 10. A cutting device according toclaim 9, wherein said motor is at least one of a hydraulic and pneumaticmotor, which is hydraulically or pneumatically connected to a separatehydraulic or pneumatic pump.
 11. A method for cutting at least one of abottom and a wall of a storage tank, comprising: independently moving acutting device over the bottom of the storage tank by way of a motorduring the cutting operation.
 12. A method according to claim 11,wherein said cutting is effected by squirting an abrasive liquid underhigh pressure against and through at least one of the bottom and thewall.
 13. A method according to claim 12, wherein said abrasive liquidcontains at least one of sand and garnet.
 14. A method according toclaim 11, wherein the cutting device is hydraulically or pneumaticallydriven, to which end a hydraulic or pneumatic pump is disposed outsidethe storage tank, which pump is connected to the motor.
 15. A methodaccording to claim 11, wherein the cutting device abuts against the wallof the storage tank while moving through the storage tank, with the wallacting as a guide.
 16. A system according to claim 1, wherein the systemis for cutting at least one of a bottom and a wall of an oil storagetank.
 17. A system according to claim 3, wherein the nozzle isspring-connected to the driven portion of the cutting device.
 18. Asystem according to claim 1, wherein the transmission ratio is such thatthe velocity of movement of the device will be less than 0.1 m/s, withat least one of an engine speed of about 3000 rpm and a hydraulic outputof about 25 l/min.
 19. A system according to claim 1, wherein thetransmission ratio is such that the velocity of movement of the devicewill be less than 0.06 m/s, with at least one of an engine speed ofabout 3000 rpm and a hydraulic output of about 25 l/min.
 20. A cuttingdevice according to claim 9, wherein the cutting device is for cuttingat least one of a bottom and a wall of an oil storage tank.